In the development of the technology of printing, considerable effort has been devoted to methods for improving the characteristics of the substrate to be printed. There are two main factors to consider in the printing of papers by any printing process; these are "runnability" and "print quality". Runnability is defined as the ability to get the sheet through the press and is important because failures in runnability cause expensive downtime on the presses. The following sheet characteristics have been found to affect runnability:
(a) Flatness, freedom from buckles, puckers, wave, and curl; PA0 (b) Trimming; PA0 (c) Dirt; PA0 (d) Moisture Content or pH; PA0 (e) Adequate pick resistance; PA0 (f) Adequate water resistance; PA0 (g) Paper-ink relationship; PA0 (h) Mechanical condition. PA0 (a) Color; PA0 (b) Brightness; PA0 (c) Opacity; PA0 (d) Smoothness; PA0 (e) Gloss PA0 (f) Refractiveness. PA0 1. Smoothness PA0 2. Levelness PA0 3. Cushion PA0 4. Ink Receptivity PA0 Temperature of organosilicon halide: 50.degree. F. to 200.degree. F. PA0 Temperature of cellulosic material: frozen to 200.degree. F. PA0 Concentration of organosilicon halide: 2% to saturation
Print quality is the effect of the paper on the accurate reproduction of the image form to be printed. The significant paper properties effecting print quality are:
Of particular interest for letterpress printing are:
To some degree, the runnability characteristics for gravure printing are considerably less stringent though the printing characteristics listed above continue to be significant.
Improvement in sheet characteristics allows greater variability in printing processes, in ink formulations, and may result in substantial improvement in image quality, economies in processing, or both. Essentially, in the case where printing is to be accomplished on a cellulosic sheet, a modification of the balance between the oleophilic and hydrophilic functionalities of the cellulose molecule has been found useful. Heretofore, improvements in sheet characteristics have been achieved through the use of additives or coatings in the manufacture of many printing or packaging grades of paper. Typical additives such as rosin, alum and the like or typical coatings such as those comprised of starch, clay, appropriate binders and brighteners, are often employed to assist printability and runnability of the substrate. These techniques are frequently costly and cumbersome and often fall wide of the mark of producing an ideal printing substrate.
For certain grades of substrates, in particular newsprint, present techniques of production and factors of the marketplace militate against the suitability of these techniques for modifying the sheet. Further, with respect to newsprint, efficiencies of operation have favored the use of web offset printing systems whose more stringent runnability requirements are barely met by newsprint as presently produced. Linting and inadequate water resistance can result in sheet breaks causing downtime and other problems of press operation.
Some producers of newsprint have installed twin-wire formers whose purpose is to produce a sheet with uniform wire and felt sides. These machine modifications are costly and involved and yet they may result in a sheet whose runnability, while improved, is far from ideal.
It is an object of the present invention to improve the printing characteristics of cellulosic substrates by a process which is eminently compatible with present manufacturing practices.
Another object of the invention is to provide a printing process of improved runnability and printing quality.
Yet another object of the invention is to provide printed products characterized by improved imaging, reduced strike-through, mottling and ink usage, faster drying and reduced linting.